Rory,
I just went out to the shop and looked at mine again. The hinge body basically has three parts. The bottom spring retaining plate spot welded to the main body, the main body if you will, and the top portion of the body which is spot welded to the main body. If your main body is rusted beyond repair like Dick suggested, you should be able to fabricate or have a local sheet metal shop bend up two new main bodies using your exisiting ones for patterns, drill a new hole in the bottom center, weld on new spring retaining plates from LICS and then weld to the top portion.
I just went out to the shop and looked at mine again. The hinge body basically has three parts. The bottom spring retaining plate spot welded to the main body, the main body if you will, and the top portion of the body which is spot welded to the main body. If your main body is rusted beyond repair like Dick suggested, you should be able to fabricate or have a local sheet metal shop bend up two new main bodies using your exisiting ones for patterns, drill a new hole in the bottom center, weld on new spring retaining plates from LICS and then weld to the top portion.